Continuous-type ink jet printing systems create printed matter by selective charging, deflecting, and catching drops produced by one or more rows of continuously flowing ink jets. The jets themselves are produced by forcing ink under pressure through an array of orifices in an orifice plate. The jets are stimulated to break up into a stream of uniformly sized and regularly spaced droplets.
The approach for printing with these droplet streams is to use a charge plate to selectively charge certain drops and to then deflect the charged drops from their normal trajectories. The charge plate has a series of charging electrodes located equidistantly along one or more straight lines. Electrical leads are connected to each such charge electrode, and the electrical leads in turn are activated selectively by an appropriate data processing system.
Conventional and well-known processes for making the orifice plate and charge plate separately consist of photolithography and nickel electroforming. Orifice plate fabrication methods are disclosed in U.S. Pat. Nos. 4,374,707; 4,678,680; and 4,184,925. Orifice plate fabrication generally involves the deposition of nonconductive thin disks onto a conductive metal substrate using photolithographic processes. Nickel is this electroformed onto the conductive metal mandrel and partial covers the nonconductive thin metal disks to form orifices. After this electroforming process, the metal substrate is selectively etched away leaving the orifice plate electroform as a single component. Charge plate electroforming is described in U.S. Pat. Nos. 4,560,991 and 5,512,117. These charge plates are made by depositing nonconductive traces on a metal substrate followed by deposition of nickel in a similar fashion to orifice plate fabrication, except that parallel lines of metal are formed instead of orifices. Nickel, which is a ferromagnetic material, is unsuitable for use with magnetic inks. Nor can low pH ink (pH of approximately 6 or less) be used with nickel, which is etched by low pH ink. As a result, nickel materials are very suited to alkaline based fluids. U.S. Pat. No. 4,347,522 discloses the use electroforming or electroplating techniques to make a metal charge plate.
An ink jet printhead having an orifice plate and a charge plate requires precise alignment of these components to function properly. For high resolution ink jet printheads this alignment process is a difficult labor intensive operation that also requires significant tooling to achieve. It is desirable to develop a printhead that would simplify the alignment of the charging electrodes and the orifices from which ink is jetted.
Accordingly, it is an object of the present invention to provide a fabrication process of the orifice plate and charge plate that permits the use of both low pH and magnetic inks. It is another object of the present invention to provide such an orifice plate and charge plate as one, self-aligned component with high yield and robust connection.